The present invention relates to a matrix switch device, which is mounted in a home receiving antenna of a digital satellite broadcasting (DSB) system and is suitable for switching input signals from a plurality of satellites.
Multi-satellite systems and multi-channel systems are increasingly used for satellite broadcasting. Therefore, as a low noise block (LNB), a matrix switch device for switching input signals from the plurality of satellites and especially a matrix switch integrated circuit, which is a matrix switch device formed as a semiconductor integrated circuit, are highly demanded. Incidentally, the LNB is a BS/CS receiving front-end mounted in the home receiving antenna of the DBS system. To this end, a 2xc3x972 matrix switch integrated circuit, which is a matrix switch device having two input terminals and two output terminals, is developed.
Hitherto, optimization of the size of the elements of the 2xc3x972 matrix switch integrated circuit has been performed for improving ON/OFF characteristics of the switch thereof. Optimization of wiring layout on the integrated circuit chip thereof has also been performed for reducing signal interference caused by dense wiring for inter-connecting the switches thereof. Further, optimization of the package thereof for mounting the 2xc3x972 matrix switch integrated circuit therein, and optimization of mounting and assembly methods have also been performed for achieving high isolation characteristics.
On the other hand, a matrix switch device is demanded, the matrix switch device being capable of receiving broadcasting signals from the plurality of satellites and switching between multiple channels, the number of channels being more than previously achieved. For example, the recently used DBS system, which receives broadcasting signals from two satellites, requires a 4xc3x972 matrix switch device for receiving and switching horizontally and vertically polarized wave signals from the satellites. An exemplary 4xc3x972 matrix switch device comprises first and second input terminals to which the horizontally and vertically polarized wave signals are input from one of the satellites, and comprises third and fourth input terminals to which the horizontally and vertically polarized wave signals are input from another satellite. A very high isolation characteristic is required between the first and second input terminals and between the third and fourth input terminals.
The above-described 4xc3x972 matrix switch device further comprises two 2xc3x972 matrix switch integrated circuits which achieve high isolation, a plurality of PIN diodes, and the mounting board. The 2xc3x972 matrix switch integrated circuits and the PIN diodes are mounted on the mounting board and are inter-connected by wiring lines on the mounting board. Other matrix switch integrated circuits and PIN diodes are disposed between the first and second input terminals and between the third and fourth input terminals where high isolation is required, and the first to fourth input terminals are inter-connected by external wiring lines. Therefore, signal interference in the wiring lines on the board is reduced and the high isolation characteristic is achieved.
The 4xc3x972 matrix switch device each comprises two PIN diodes on four circuit wiring lines, that is, eight PIN diodes in total. The PIN diodes, however, requires high isolation for signals transmitted in the reverse direction (from the output direction to the input direction). Therefore, the PIN diodes must be disposed in series. Accordingly, the number of parts of the existing 4xc3x972 matrix switch device is at least ten. This large number of parts results in a mounting board with an increased area and an increased number of assembly-adjusting procedures. Accordingly, the cost of the 4xc3x972 matrix switch device also increases.
In view of the above, a low-cost 4xc3x972 matrix switch integrated circuit should be developed. This 4xc3x972 matrix switch integrated circuit comprises twelve switches for example. The control voltage of the switches is set to a suitable level so that the first and second output terminals thereof can separately select and switch the input signals.
As in the case of the 2xc3x972 matrix switch integrated circuit, optimization of the size of the elements of the 4xc3x972 matrix switch integrated circuit is performed for increasing the ON/OFF characteristics of the switches. Optimization of the wiring layout on the IC chip thereof is also performed for reducing signal interference caused by dense wiring for inter-connecting the switches. Further, optimization of the package thereof for mounting the 4xc3x972 matrix switch integrated circuit therein, and optimization of mounting and assembly methods are also performed for increasing the isolation characteristic.
However, since the number of switches of the 4xc3x972 matrix switch integrated circuit is increased, the amount of wiring lines for inter-connecting the switches becomes twice as much as that of the 2xc3x972 matrix switch integrated circuit. Further, the wiring line on the integrated circuit chip becomes complicated due to the increased number of D lines for the switches. Subsequently, the distance between the switches on the integrated circuit chip decreases, and the density and crossovers of the signal wiring lines increase more than in the case of the 2xc3x972 matrix switch integrated circuit. Since the signal interference is not sufficiently reduced, the isolation of the 4xc3x972 matrix switch integrated circuit does not easily increase.
Keeping sufficient distances between the switches (FET) and the signal wiring line is effective for decreasing the signal interference. However, this method may result in a semiconductor integrated circuit chip with an increased size and an increased cost of the switches. In such a case, a large-sized package will be required according to the increased size of the semiconductor integrated circuit chip. However, manufacturing a new production line for such packages will significantly increase the cost of the switches.
Accordingly, the object of the present invention is to provide a matrix switch device comprising a semiconductor integrated circuit chip functioning as a satellite reception unit having high isolation between the terminals thereof and that is small and susceptible of low cost of manufacture because of the reduced number of elements thereof.
A matrix switch device according to a first aspect of the present invention comprises a semiconductor integrated circuit chip. The semiconductor integrated circuit chip comprises a 2xc3x972 matrix switch having two input terminals and two output terminals, and an SPDT (Single Pole Double Throw) switch at a stage subsequent to the 2xc3x972 matrix switch, which has two input terminals and one output terminal. Electrical connection is performed between one of the output terminals of the 2xc3x972 matrix switch and one of the input terminals of the SPDT switch. The two input terminals and the other of said output terminals of the 2xc3x972 matrix switch, and the other input terminal and the output terminal of the SPDT switch are led out of the semiconductor integrated circuit chip.
A matrix switch device according to a second aspect of the present invention comprises a semiconductor integrated circuit chip. The semiconductor integrated circuit chip comprises a 2xc3x972 matrix switch having two input terminals and two output terminals, and an SPDT switch at a stage subsequent to the 2xc3x972 matrix switch, which has two input terminals and one output terminal. The input terminals and the output terminals of the 2xc3x972 matrix switch, and the input terminals and the output terminal of the SPDT switch are led out of the semiconductor integrated circuit chip.
A 4xc3x972 matrix switch device according to a third aspect of the present invention comprises a first matrix switch unit comprising the above-described matrix switch device packaged in a first package and a second matrix switch unit comprising the matrix switch device packaged in a second package. The 4xc3x972 matrix switch device further comprises a first external wiring line and a second external wiring line. Electrical connection is performed between the other of said output terminals of the 2xc3x972 matrix switch of the first matrix switch unit and the other of said input terminals of the SPDT switch of the second matrix switch unit via the first external wiring line outside the first and second packages. Electrical connection is also performed between the other of said output terminals of the 2xc3x972 matrix switch of the second matrix switch unit and the other of said input terminals of the SPDT switch of the first matrix switch unit via the second external wiring line outside the first and second packages.
The other objects of this invention will become clear as the description proceeds.